The present invention relates to a method and a measuring apparatus for checking a circuit devised for contactless data communication, which comprises an antenna and an electronic component coupled with the antenna.
The checking of the circuit can relate to both electronic properties of the circuit and the functionality of the circuit or individual parts of the circuit.
Portable data carriers, such as national identity cards, passports, credit cards, labels for authenticating goods or the like, can be equipped with an antenna, for example in the form of an antenna coil, for contactless data communication with a reading device. The antenna coil is thus as a rule connected to an electronic component of the data carrier, in particular a chip, and applied, for example imprinted, on a carrier layer or inlay layer, for example made of a plastic material such as PC or PVC, of a data-carrier body of the data carrier.
Alternatively, a corresponding circuit can also be devised to be integrated into an end device, such as a mobile radio end device, a smartphone or a reader. The circuit can in particular be designed as an RFID or NFC module which is intended to be firmly integrated into an end device of the stated kind.
To check the functionality of an antenna coil during or after the manufacture of the corresponding data carrier or device, various methods are known. Such a check substantially involves checking whether the antenna coil has a break and/or whether two or more coil turns of the antenna are inadvertently short-circuited. Defects of this kind considerably impair the functionality of the antenna coil, or destroy it completely. A check of the circuit, consisting of the antenna and the electronic component connected to the antenna, can also relate to the functionality of the component or of individual parts of the component, as mentioned hereinabove.
Concurrently with production, a check of the antenna coil has hitherto usually been effected in the form of a direct-current resistance measurement. Such a checking method is elaborate, since a contacting of the antenna coil is required. Further, only certain defects of the checked circuit can be recognized. A malfunctioning of one or more parts of the electronic component or a conducting path break in certain regions of the antenna are not, or hardly, recognizable in this manner.
Alternatively, the resonance frequency of the antenna coil and its quality factor can be determined contactlessly. For this purpose, a phase and impedance analyzer is employed as a rule. Such a, very elaborate, method is described in detail for example in “RFID-Handbuch” by Klaus Finkenzeller, 6th edition, Carl Hanser Verlag, Munich, 2012, in chapter 4.1.11.2. When the measured resonance frequency lies in a pre-specified range, the antenna coil is functional. This kind of check is more informative than a purely ohmic measurement, but far more elaborate and best carried out manually. The time duration of such a check lies in the range of several seconds. Hence, this check is not carried out concurrently with production as a rule, but merely on some random samples and for production release. Further, properties of the analyzer, for example the impedance of a measuring antenna, can influence the result of the measurement. Different analyzers hence lead to deviating measuring results as a rule.